Image MIME Reference
PBM
Portable Bitmap
image/x-portable-bitmap
VS
GIMP Image Format
image/x-xcf
XCF
A complete technical comparison of Portable Bitmap and GIMP Image Format — covering compression, feature support, browser compatibility, magic bytes, and when to choose each format.
Equal browser support
Feature Support
| Feature | PBM | XCF |
|---|---|---|
| Transparency (Alpha) | ✕ No | Yes |
| Animation Support | ✕ No | Yes |
| Progressive Loading | ✕ No | ✕ No |
| HDR Support | ✕ No | Yes |
| EXIF Metadata | ✕ No | Yes |
| ICC Color Profile | ✕ No | Yes |
Portable Bitmap
image/x-portable-bitmap
Extension
.pbm
Container
Netpbm
Compression
Uncompressed
Algorithm
None
Color Depth
1-bit (Monochrome)
Developed by
Jef Poskanzer (Netpbm Project)
Released
1988
Magic Bytes
50 31 (ASCII) or 50 34 (Binary)
GIMP Image Format
image/x-xcf
Extension
.xcf
Container
GIMP Hierarchical Chunk Container
Compression
None / RLE (Run-Length Encoding) / Zlib / Deflate (In newer GIMP versions)
Algorithm
NoneRLEZlib
Color Depth
8-bit per channel, 16-bit per channel, 32-bit floating point
Developed by
Spencer Kimball, Peter Mattis, and the GIMP Development Team
Released
1995
Magic Bytes
67 69 6D 70 20 78 63 66
Browser Support Comparison
| Browser | PBM | XCF |
|---|---|---|
Chrome
|
✕ | ✕ |
Firefox
|
✕ | ✕ |
Safari
|
✕ | ✕ |
Edge
|
✕ | ✕ |
IE (Legacy)
|
✕ | ✕ |
PBM
PBM Strengths
- Absolute structural simplicity allows parsers to be written from scratch with just a few lines of code
- ASCII encoding allows manual editing and debugging directly within a standard text editor
- Serves as a flawless, lossless intermediary for 1-bit raster data like scanned documents or barcodes
Limitations
- Strictly limited to 1-bit monochrome images; cannot natively display shades of gray or color
- Lack of compression results in extremely large file sizes, particularly when using the ASCII 'P1' encoding
- No support for alpha transparency or modern metadata standards like EXIF
XCF
XCF Strengths
- Preserves all non-destructive editing elements, layer hierarchies, masks, and alpha channels across GIMP sessions
- Open and thoroughly documented specification within the open-source community, allowing third-party tools like Krita and ImageMagick to read project files
- Reliable magic byte header prevents misidentification
Limitations
- Massive file sizes because raw, unflattened layer bitmaps and masks are stored directly within the project archive
- Completely proprietary to the GIMP ecosystem for deep editing; cannot be natively rendered or parsed by web browsers
- Third-party software supporting XCF may occasionally struggle to render complex text layer adjustments or advanced layer blend modes identically to GIMP
When to choose which format
PBM
Use PBM when…
- Optical Character Recognition (OCR) Pre-processing
- Unix/Linux Command-Line Image Pipelines
- Academic Image Processing Teaching
XCF
Use XCF when…
- GIMP Native Project Archival
- Layered Photo Editing and Graphic Design
- Intermediary Asset Preparation for Export